Fix missing-docs lint on dummy build.rs

This ensures the dummy `build.rs` (which contains an empty `main()`
function) passes the `missing-docs` lint check from rustc

Fixes #377

Author: nmattia

lib.nix

@@ -191,15 +191,21 @@ rec
                 pushd $out/$member > /dev/null
                 mkdir -p src
 
-                # Avoid accidentally pulling `std` for no-std crates.
-                echo '#![no_std]' >src/lib.rs
-
                 # pretend there's a `build.rs`, otherwise cargo doesn't build
                 # the `[build-dependencies]`. Custom locations of build scripts
                 # aren't an issue because we strip the `build` field in
                 # `fixupCargoToml`; so cargo always thinks there's a build
                 # script which is `./build.rs`.
-                echo 'fn main() {}' > build.rs
+                # We also add documentation to avoid rustc complaining about
+                # missing documentation: https://github.com/nix-community/naersk/issues/377
+                echo '//! stub crate' > build.rs
+                echo '/// stub main function' >> build.rs
+                echo 'fn main() {}' >> build.rs
+
+                # Avoid accidentally pulling `std` for no-std crates.
+                echo '//! stub lib' >src/lib.rs
+                echo '#![no_std]' >>src/lib.rs
+
                 popd > /dev/null
             done
 

test/fast/default.nix

@@ -12,6 +12,7 @@
   git-dep-dup = pkgs.callPackage ./git-dep-dup { inherit naersk; };
   git-single-repository-with-multiple-crates = pkgs.callPackage ./git-single-repository-with-multiple-crates { inherit naersk; };
   git-symlink = pkgs.callPackage ./git-symlink { inherit naersk; };
+  stub-lints = pkgs.callPackage ./stub-lints { inherit naersk; };
   openssl = pkgs.callPackage ./openssl { inherit naersk; };
   post-install-hook = pkgs.callPackage ./post-install-hook { inherit naersk; };
   readme = pkgs.callPackage ./readme { inherit naersk; };

test/fast/stub-lints/default.nix

@@ -0,0 +1,13 @@
+{ naersk, ... }:
+
+naersk.buildPackage {
+  src = ./fixtures;
+  doCheck = true;
+
+  # we instruct cargo to error out if the 'missing-docs' lint is triggered. At the time of writing
+  # (30-01-2026) this is the only documentation lint that rustc looks for:
+  #
+  # > Note that, except for missing_docs, these lints are only available when running rustdoc, not rustc.
+  # > [https://doc.rust-lang.org/rustdoc/lints.html#lints]
+  CARGO_BUILD_RUSTFLAGS = "-D missing-docs"; # error out if 'missing-docs' is triggered
+}

test/fast/stub-lints/fixtures/Cargo.lock

@@ -0,0 +1,10 @@
+# Tests that the stub/dummy "build.rs" does not fail on rustc lints
+# https://github.com/nix-community/naersk/issues/377
+
+[package]
+name = "stub-lints"
+version = "0.1.0"
+authors = ["nicolas <nicolas@nmattia.com>"]
+edition = "2018"
+
+[dependencies]

test/fast/stub-lints/fixtures/Cargo.toml

@@ -0,0 +1,6 @@
+//! Hello world!
+
+/// Says hello
+fn main() {
+    println!("Hello, world!");
+}